High energy density materials (HEDMs) are a new class of energetic materials that exhibit a high energy density. Their explosive power, derived from high heats of formation obtained from breaking stable C—N and N═N bonds during combustion or detonation, allows for the use of smaller quantities of explosives to achieve the same energy output as current energetics. Of importance are new melt-cast compounds that are being developed as an alternative to TNT (2,4,6-trinitrotoluene) or Composition B (consisting of castable mixtures of RDX-1,3,5-trinitroperhydro-1,3,5-triazine and TNT). Many of these new melt cast candidates are high density aromatic heterocycles containing nitro and nitroso moieties that are oxidized in the final step of synthesis from their corresponding amines.
Current procedures for making HEDM has long been a concern in energetic synthetic chemistry because of dangerous reaction conditions. Procedures to oxidize inert starting materials with primary amines typically require concentrated peroxides, acids and large amounts of transition metals. For instance, 1-methyl-3,5-diamino-1H-1,2,4-triazole is nitrated under acidic conditions using concentrated H2SO4 and NaNO2 to form 1-methyl-3,5-dinitro-1H-1,2,4-triazole (MDNT). 3,4-Bis(3-nitrofurazan-4-yl)furoxan (BNFF aka DNTF) is nitrated from the corresponding diamine compound using 96% H2SO4. In addition to the corrosive properties, dangerous handling and disposal of the acidic chemicals, these nitration reactions exhibit powerful exotherms that are difficult to control and prevent any scale-up efforts due to safety concerns. Thus, a need exists for compounds that can aid in a safer oxidation of amine groups during synthesis of energetic compounds.
Catalysts are a class of compounds that accelerates chemical reactions, without itself undergoing a permanent chemical change by lowering the activation energy of the reaction. They may be characterized as either exhaustive or reusable. Exhaustive reactions also referred to as stoichiometric reactions require a continuous or excess supply of catalysts as the catalyst is consumed as part of the reaction. Rose Bengal is an example of such a catalyst.
In contrast, renewable catalysts can be reused or regenerated during a reaction but may require higher activation energy to complete a reaction.
Catalysts are also categorized by their phasic compatibility with the reaction agents. Those catalysts that are in the same phase as the reactants are deemed homogenous catalysts while those in a different phase are heterogeneous. Homogenous catalysts, intimately mixed with the reactants, will generally provide higher chemical activity via lower effective activation energies. This may create a problem with separating such potentially useful materials from the desired products into which they are mixed or leaching of the catalyst metal center in the solvent environment. Leaching of the metal center presents substantial difficulty in isolating the dissolved metal catalyst or generate harmful undesired secondary products that may occur from use. As an example use of sodium tungstate in stoichiometric quantities when synthesizing BNFF results in great difficulty isolating leached catalyst from the desired product.
Heterogeneous catalysts, however, will generally not exhibit such high activity (activation energies), but it can easily be separated from the reactants, oftentimes by simple physical filtration. However depending on the reaction heterogeneity does not always guarantee resolution to leaching of the metal. Chemical modification of the metal center may prevent leaching in either homogeneous or heterogeneous physical states.
Hybrid catalysts are therefore created to capture the high catalytic activity of homogenous catalysts but also the separation ease of a homogenous catalyst. Some prior art composites solve this problem by coupling the catalysts to solid state supports such as metal oxides, for example titanium oxides. These hybrid metal oxide catalysts, however, when activated by light creates reactive oxygen species which indiscriminately attack C—H bonds leading to self-deactivation.
Thus, a need arises for catalytic materials that can catalyze oxidation of amines in energetic synthesis, having high catalytic activity that can be readily isolated from a solution, reduces or eliminates leaching into relevant environment, and not self-decompose.